1. Field of the Invention
The present invention relates to a process cartridge, a method for assembling a process cartridge and an image forming apparatus having the cartridge. The image forming apparatus may be, for example, a laser beam printer, an LED printer, an electrophotographic copying machine, a facsimile machine, a word processor or the like.
2. Related Background Art
In image forming apparatuses such as printers, a latent image is formed by selectively exposing a photosensitive drum (image bearing member) which has been uniformly charged, and the latent image is then visualized with toner as a toner image which is in turn transferred onto a recording sheet, thereby recording an image on the recording sheet. In such apparatuses, whenever the toner is consumed or used up, new toner must be replenished. However, the toner replenishing operation not only is troublesome, but also often causes the contamination of its surroundings. Further, the maintenance of various elements must be performed periodically.
To this end, a so-called process cartridge wherein a photosensitive drum, a charger, a developing device, a cleaning device and the like are integrally contained in a cartridge housing which can be removably mounted to an image forming apparatus, whereby the replenishment of toner or the exchange of parts whose service lives been have been expired can be accomplished and the maintenance of the apparatus can be facilitated has been proposed and put into practical use (for example, as disclosed in U.S. Pat. Nos. 3,985,436, 4,500,195, 4,540,268 and 4,627,701).
The cartridge housing is constituted by combining a plurality of frames such as a toner frame for containing toner, a developing frame for supporting the developing device and a cleaning frame for supporting the cleaning device. A frame for supporting the photosensitive drum and a developing sleeve is formed by injection-molding polyphenylene ether (PPE) or polyphenylene oxide (PPO) which has good mechanical features such as good bending strength. On the other hand, the toner frame for containing the toner may be made of polystyrene resin (PS) which has relatively poor mechanical features such as low bending strength but is inexpensive, because this frame does not support any heavy part such as the photosensitive drum.
The toner frame and the developing frame are joined to each other by the ultrasonic welding. However, since these frames are made from different materials, there arises dispersion in welding strength, thereby worsening the reliability of the welding.
Further, recently, it has been proposed to collect the used cartridges for the recycle. In this regard, when the frames are crushed to reuse them as material for forming new frames, if the frames are not separated from each other and plural frames are crushed together, since the frames are made from different materials, the different materials are mixed, thus deteriorating the mechanical features of new frames. However, since the toner frame is welded to the developing frame, there arises a problem that it takes a long time to separate these frames.
Further, toner carrier particles for carrying the toner are generally made of styrene group resin. Accordingly, since the material of the carrier particles is different from the material of the developing frame, if the developing frame with waste toner adhered thereto is crushed for recycle, the different materials are mixed, thereby deteriorating the mechanical features, as in the aforementioned case. Thus, in the recycle, the waste toner must be completely removed from the developing frame. This cleaning operation is very troublesome.